All known calcitonin gene related peptide ("CGRP") analogs share some common structural features. Each is 37 amino acids long with a C-terminal phenylalanine amide and an N-terminal disulfide linked ring from position 2 through position 7. One of the human CGRP's, for example, has the following formula (Morris, H. R. et al. (1984) Nature 308, 746-748) ##STR1## A second recently characterized human CGRP differs from the above by having the amino acid Asn at position 3, Met at position 22 and Ser at position 25 (Steenbergh, P. H. et al. (1985) Febs Lett. 183, 403-407).
There are also two known CGRP of rat origin. The first to be characterized differs from the human sequence above by having Ser at position 1, Asn at position 3, Asp at position 25 and Glu at position 35 (Amara, S. G. et al. (1982) Nature, 298, 240-244). A recently characterized second rat CGRP differs from the human structure by having Ser at position 1, Asn at position 3, and Asp at position 25 (Amara, S. G. et. al., Science 229, 1094-97, 1985).
It has been shown that CGRP and calcitonin are derived from the same gene. The calcitonin gene is alternatively expressed in a tissue specific fashion producing either the calcium-regulating hormone calcitonin in the thyroid or the neuropeptide CGRP in the brain (Rosenfeld, M. G. et al. (1983) Nature 304, 129-135). Recently, it has been shown that both peptides are produced in thyroid parafollicular cells (Lee, Y. et al. (1985) Neuroscience 15, 1227-1237; Self, C. H. et al. (1985) Peptides 6, 627-630) which indicate a peripheral physiological role. Both calcitonin and CGRP interact with the same receptor in some experimental conditions, thus showing that both peptides share some common structural features (Goltzman, D. and Mitchell, J. (1985) Science 227, 1343-1345; Wohlwend, A. et al. (1985) Biochem. Biophys. Res. Commun. 131, 537-542). The inhibition of gastric acid secretion by both peptides also confirms such similarities (Hughes, J. J. et al, (1984) Peptides 5, 665-667; Stevenson, J. C. (1985); Clin. Endocrinol. 22, 655-660; Lenz, H. J. et. al., (1985) Gut 26, 550-555). CGRPs are potent vasodilators; a property that has not been detected in human calcitonin (Brain, S. D. et al. (1985) Nature 313, 54-56). U.S. Pat. No. 4,530,838 discloses two naturally occurring rat CGRPs and U.S. Pat. No. 4,549,986 discloses human CGRP.